Electric lamp

ABSTRACT

The electric lamp comprises a lamp vessel ( 1 ) having an end portion ( 3 ) which is surrounded by a shell portion ( 22 ) of a lamp cap ( 20 ) having screw thread. The end portion ( 3 ) has transversal indents ( 6 ). A plastic coupling member ( 30 ) having arms ( 33 ) bearing a cam ( 31 ) on their inner surface ( 34 ) and being undulated at their outer surface ( 35 ) is present in the lamp cap ( 20 ). The cams ( 31 ) are located in a respective indent ( 6 ). The shell portion ( 22 ) of the lamp cap ( 20 ) is screwed onto the coupling member ( 30 ). In the electric lamp, the lamp cap ( 20 ) is fitted to the lamp vessel ( 1 ) by assembling. The current conductors ( 7, 8 ) too may be connected to the contacts ( 21 ) of the lamp cap ( 20 ) by assembling, thus avoiding time and energy-consuming thermal processes.

The invention relates to an electric lamp equipped with:

a blown-glass lamp vessel having an axis and, around said axis, an endportion with an end where the lamp vessel and a stem extending in thelamp vessel are fused together, which end portion has indentations at adistance from the end, which indentations extend transversely to theaxis;

an electric element in the lamp vessel, which electric element isconnected to current conductors which issue from the lamp vessel to theexterior via the stem;

a lamp cap with electric contacts, a metal shell portion which isundulated so as to form screw thread, and a base portion with at leastone of the electric contacts, the shell portion being present around theend portion and the base portion extending transversely to the axis, andthe current conductors each being connected to a respective one of theelectric contacts; and

a coupling member provided with cams in the lamp cap, which cams engagein a respective indentation, and which coupling member is secured to thelamp cap.

An embodiment of such an electric lamp is known from U.S. Pat. No.4,496,874.

In the known lamp, the coupling member is an open ring of metal stripwhich largely surrounds the end portion and which is provided withprojections which serve as cams that engage in the indentations of thelamp vessel. The open ring has tongues which press against the end ofthe lamp vessel and which serve to keep the ring fixed in the axialdirection during mounting of the lamp cap. The lamp cap is secured tothe ring by welding using a laser.

In the case of commercially available lamps having a blown-glass lampvessel, the lamp cap is customarily secured to the lamp vessel by meansof cement. In these lamps, the indentations in the end portion of thelamp vessel serve to make sure that the cement gets a grip on the lampvessel. Particularly in the case of lamps having an Edison lamp cap,which must be rotated around their axis a number of times to screw thelamp into the lamp holder and make electric contact with said lampholder, but also in the case of bayonet lamp caps, which only have to berotated one quarter of a turn, high requirements are imposed on thestrength of the cement joint. Also if the lamp must be removed from theholder after a large number of operating hours, the cement must besufficiently strong to withstand the resistance exerted by the lampholder during rotation of the lamp.

A drawback of cement, particularly if the lamp has burned atcomparatively high temperatures, resides in that it may have becomebrittle as a result of which the connection between the lamp vessel andthe lamp cap may be lost. As a result, the lamp cap may be retained inthe lamp holder when the lamp is being removed from the lamp holder.When the loose lamp cap is removed from the lamp holder, there is a riskof electric shocks.

Another drawback of the use of cement to secure the lamp cap resides inthat the through-hardening of the cement after the lamp cap has beenprovided requires much thermal energy and much time. If high-speedproduction machines are used to manufacture incandescent lamps, the unitfor mounting the lamp cap is embodied so as to be a double unit to keepup with the rate of supply of finished lamp vessels.

In spite of the drawbacks involved in the use of cement, and althoughthe cement-free lamp described in the opening paragraph was proposed aslong as twenty years ago, and other proposals for cement-free lamps areof a much more recent date, indicating that there is long-felt need forlamps having a lamp cap that is secured in a cement-free manner, thelamp cap of lamps having a blown-glass lamp vessel is still mountedusing cement. This can be attributed to drawbacks attached to thecement-free construction described in the opening paragraph and tosimilar, older constructions.

A first drawback of the known lamp described hereinabove resides in thatthe metal coupling member locally exerts large forces on the lamp vesselduring placing the lamp in or removing the lamp from a lamp holder,which forces may cause fracture of the lamp vessel. Another drawbackresides in that the connection between the lamp vessel and the lamp capis not a rigid connection, and the lamp cap remains movable. Yet anotherdrawback resides in that securing the lamp cap requires the couplingmember to be provided with welded joints. As the coupling member is notvisible through the lamp cap, and it cannot be observed whether thecoupling member actually contacts the lamp cap at the location of awelding operation, there is no certainty as to the effectiveness of thewelding operation.

It is an object of the invention to provide an electric lamp of the typedescribed in the opening paragraph, wherein the lamp cap is firmlyconnected to the lamp vessel without applying cement or a thermaloperation, and wherein the risk of fracture of the lamp vessel due tolocally exerted forces is effectively counteracted.

In accordance with the invention, this object is achieved in that thecoupling member is a plastic synthetic resin body having

a central portion transverse to the axis, and

arms which are distributed around the axis and extend from the centralportion in the axial direction, which each support at an inner surface arespective one of the cams, and which have an undulatory profile at anouter surface, which undulatory profile is in engagement with the screwthread of the lamp cap.

As the coupling member is made of a plastic synthetic resin, it iscapable of deformation in the case of a very local contact with the lampvessel, resulting in a comparatively large contact surface and hence areduction of local contact pressure. In addition, the synthetic resinenables the coupling member to have cams whose shape largely correspondsto the shape of the indentations, so that they have a large contactsurface with said indentations, resulting in a firm coupling between thelamp vessel and the lamp cap.

When the lamp vessel is finished and the lamp cap must be mounted, thecoupling member is provided around the end portion by moving it axiallytowards said end portion and snapping it on to it such that the cams arein the indentations. Next, the lamp cap is screwed down on the couplingmember, so that the coupling between the lamp cap and the lamp vessel isbrought about without thermal treatment, and the lamp cap is firmlyfixed in position. After the current conductors subsequently have beensecured to the contacts, the lamp can be put into operation.

In order to secure the lamp cap against relative rotation, the lamp capmay be locally indented, for example in an indentation in the couplingmember or between the arms of the coupling member. Alternatively, it ispossible to provide the coupling member with tangential teeth, forexample, at the location of the cams at its outer surface and to providetongues, which are pressed inwards, inside the shell portion of the lampcap, for example, at a distance from its end that is situated near thelamp vessel, which tongues rattle over the teeth when the lamp cap isscrewed on, and engage in a respective tooth in the end position of thelamp cap so as to form a snap connection. The demands imposed on thetongues are very small because they only have to catch the lamp capduring the rotatory movement taking place when the lamp is removed fromthe lamp holder, and they are loaded predominantly in their longitudinaldirection in this process. As the coupling member is situated in theimmediate vicinity of the tongues, the latter can be short, as a resultof which they are strong in the longitudinal direction.

The arms of the coupling member having said undulatory profile can beused to jointly form a, possibly interrupted, helical profile, however,a helical profile is not necessary to be able to screw the lamp cap withits screw thread onto the arms so as to be in engagement therewith.

Although the coupling member may have only two arms with cams, it isfavorable for the coupling if the coupling member has at least threearms. In the latter case, these arms are preferably distributed aroundthe axis through angles of 120 degrees. The coupling member mayalternatively have four arms which are, for example, distributed aroundthe axis through angles of 90 degrees, or arranged in pairs that lieopposite to each other, such that the arms of each pair include an angleof 60 degrees with respect to the axis. Alternatively, it is alsopossible that there are six arms which are uniformly distributed aroundthe axis. It is favorable for the lamp vessel to have six indentationswhich are uniformly distributed around the axis. In this case, in thecourse of the manufacture of the lamp, after the lamp vessel has beenheated near its end portion to the point where softening occurs, thelamp vessel can be indented using, for example, two identical tools andsubsequently inflated against said tools by means of a gas so as to formthe indentations. As a result, when the coupling member having three,four or six arms, which are mutually positioned as describedhereinabove, is provided, said coupling member does not have to beaccurately aligned with respect to the lamp vessel in order toautomatically find its proper place.

In a favorable embodiment, the central portion of the coupling member isthe base portion of the lamp cap. This embodiment has the importantadvantage that the use of a conventional lamp cap composed of a metalshell portion and a glass base portion which are fused together isprecluded. The manufacture of a conventional lamp cap is expensive owingto the use of molten glass and requires more metal than would benecessary for the mechanical strength of the lamp cap, in particular ifaluminum is used as the metal. This can be attributed to the fact thatthe metal is softened by the comparatively high temperature to which theshell portion is exposed during the provision of the base portion ofliquid glass, as a result of which the shell portion must becomparatively thick to be sufficiently strong, for example 0.22 mminstead of for example 0.19 mm.

This embodiment enables the shell portion of the lamp cap near thesynthetic resin base portion to be indented, for example into a recess,in order to lock the shell against relative rotation.

The embodiment additionally enables a snap connection to be presentbetween the coupling member and the shell portion of the lamp cap, whichsnap connection locks the shell portion against rotation.

The shell portion of the lamp cap has an end portion on the side remotefrom the lamp vessel, and the coupling member may have first axiallydirected, elastic tongues with hooks which embrace said end portion soas to form the snap connection. After it has been mounted, the shellportion of the lamp cap does not have to be deformed in order topreclude rotation. Also processing of said shell portion to form tonguescapable of engaging with teeth of the coupling member is thus precluded.

In a modification, the central portion of the coupling member has anaxially directed meandering wall in folds of which the first axiallydirected elastic tongues are arranged. In different parts of the world,lamp holders of very different construction are used which are allintended however to accommodate a lamp cap of the same shape and size.Among them are lamp holders having a contact member intended toelectrically contact the shell portion of the lamp cap, which contactmember is arranged on the bottom of the lamp holder. During mounting thelamp in accordance with the invention in, or removing it from, such alamp holder, such a contact member could be caught by an elastic tongueand annihilate the grip of the tongue's hook on the shell portion. Inthe modification described herein, this risk is counteracted.

In an attractive modification of the embodiment wherein the centralportion of the coupling member is the base portion of the lamp cap, thecentral portion of the coupling member has a seating for a metal buswhich serves as the electric contact.

In this modification, the electric contact can be provided after themanufacture of the coupling member, and it is not necessary to load themold wherein the coupling member is formed with the contact memberbefore said mold is filled with synthetic resin. The use of a metal busas the electric contact is attractive because it can be firmly anchoredin the synthetic resin. For this purpose, a slit may be present in thesynthetic resin wherein the upright wall of the bus is clamped.

The metal bus of the electric contact may have a flaring edge, and thecoupling member may have second, axially directed elastic tongues withhooks that embrace said edge so as to form the snap connection. Thisconstruction provides very good retention for the electric contact.

The relevant current conductor may be clamped between the electriccontact and the coupling member. For example during placing the electriccontact, the current conductor may have been entrained by the electriccontact into the seating for the contact, so that the current conductoris clamped in the radial direction by the coupling member and thecontact. In the above-mentioned construction having two elastic tongues,a good electric contact can be achieved already if the current conductorextends below the electric contact, over an end face of the couplingmember as, in this case, a pulling force is exerted on the electriccontact causing it to be held in contact with the coupling member in theaxial direction, and the current conductor is clamped, possibly also, inthe axial direction.

In a conventional lamp cap, the contact has an opening that connects toa channel in the base portion, through which the relevant currentconductor issues to the exterior in order to be soldered around theopening. The opening must be narrow to preclude liquid solder fromentering. Due to this, it is difficult to pass the current conductorthrough the opening when the lamp cap is being threaded on the lampvessel. In the embodiment of the lamp in accordance with the inventiondescribed herein, the base portion may have a large opening throughwhich the current conductor can be passed. This is an importantadvantage of the embodiment. It is also an important advantage that thecurrent conductor is secured to the contact by assembling, which meansin the case of an electric lamp, without welding or soldering.

In a particular embodiment, one of the current conductors is wrappedaround at least one of the arms of the coupling member in the directionof the screw thread of the shell portion of the lamp cap and is clampedbetween said arm and the shell portion of the lamp cap so as to form acontact thereof. Connecting a current conductor to the shell portion ofa lamp cap by soldering is difficult and, particularly in the case of analuminum lamp cap, not very reliable. In the customary productionmachines, the lamp in the making is positioned such that the axisextends in the vertical direction. To form a soldered joint and the lampcap, which customarily extends over the upper edge of the shell portion,along the lamp vessel and then issues from the lamp cap to the exterior,solder flux must first be provided on a vertical face and after thatsolder must be provided. In this process, there is a risk that theseliquids flow away from the location where they are needed, so that it ispossible that the connection, if any, is insufficient.

In the embodiment of the lamp in accordance with the invention, whereinthe coupling member has a seating for the relevant contact, and bothcurrent conductors are held in a fixed position by the contacts, it isexclusively through assembly that the lamp is provided with the lamp capand also with connections between the current conductors and thecontacts. Thermal processes have not been used. This leads to asubstantial reduction of the production time and a very substantialreduction in energy consumption as compared to the production time andenergy consumption involved in the mounting of the lamp cap ofconventional lamps. An additional important advantage resides in thatsolder-free lamps also essentially are lead-free lamps, and that fluxand solder vapors are avoided in the production process.

The shell portion of the lamp cap may be made of a copper alloy such as,for example, brass or tombac, although aluminum may alternatively beused. The embodiment of the lamp in accordance with the inventionwherein the relevant current conductor is connected to the shell portionby clamping the former, has the additional substantial advantage thataluminum alloys may be used, which have the advantage that they arestronger, but which cannot be used to form soldered joints. For exampleAlMg₃, which is a strong aluminum alloy comprising 3% by weightmagnesium, can be used in a thickness of, for example, 0.15 mm, whereasa mechanically comparatively weak alloy comprising more thanapproximately 1.5% by weight Mg and/or more than 5% by weight Si alreadyis incapable of being soldered. The soldered aluminum lamp caps whichare currently commercially used are made of Al 3004 and have thefollowing composition: 0.8-1.3% by weight Mg, 1.3-1.5% by weight Mn,0.7% by weight Fe, 0.5% by weight Si and 0.2% by weight Cu, and the restis aluminum.

The metal bus that can be used as a contact at the base portion may beobtained from the waste material that results from the manufacture ofthe shell portion from metal band at the location where the base portionmust be provided.

The electric lamp in accordance with the invention may have an Edisonlamp cap or a bayonet lamp cap. In the latter case, the lamp has asecond electric contact at the base portion if the lamp is intended formains-voltage operation. The shell portion of the bayonet lamp cap isundulated so as to form screw thread. This is permissible since, in thecase of bayonet lamp caps, only the diameter, the axial length and thelocation and size of the bayonet pins are standardized, while the shapeof the shell portion is not. It is sufficient if the area of the shellportion that connects to the lamp vessel is provided with screw thread.

The electric lamp in accordance with the invention may be, for example,an incandescent lamp, such as an incandescent lamp for general lightingpurposes, or a reflector lamp, in which case the electric element is anincandescent body. It is alternatively possible that the electricelement is an incandescent body in an inner envelope filled with ahalogen-containing gas. It is also possible for the electric element tobe an electrode pair in an ionizable gas, whether or not in an innerenvelope of, for example, quartz glass.

The lamp vessel may be evacuated or filled with gas. The powerconsumption of the lamp during operation at the design voltageinfluences the temperature of the lamp cap. Said temperature may be, forexample, 210 degrees Celsius in the case of a gas-filled 100 Wincandescent lamp. In the case of a 15 W lamp having an evacuated A60lamp vessel, i.e. a pear-shaped lamp vessel with a largest diametertransverse to the axis of 60 mm, the temperature of the lamp cap duringoperation is below approximately 80 degrees Celsius.

The temperature of the lamp cap during operation is important in respectof the choice of the synthetic resin to be used for the coupling member.For a comparatively high temperature use can be made, for example, ofLiquid Crystalline Polymer (LCP) filled with for example 30% by weightof, for example, glass fiber, which is commercially available under thename Zenith 6130 from Dupont. Alternatively, filled polybutyleneterephtalate (PBTP) may be used. Other synthetic resins that may be usedare, for example, polyethylene butylene terephtalate, polyether imide,polyether sulfone, polypropylene oxide, polyphenylene sulfide, polyamideimide, polyimide.

An embodiment of the electric lamp in accordance with the invention isshown in the drawing.

In the drawing:

FIG. 1 is a side elevation of a lamp;

FIG. 2 is a sectional view of the lamp vessel taken on the line II-II inFIG. 1;

FIG. 3 is a diagrammatic longitudinal sectional view of the lamp cap;

FIG. 4 is a diagrammatic view of the lamp cap taken on the line IV-IV inFIG. 1; and

FIG. 5 is a perspective view of an embodiment of the coupling member.

In FIG. 1, the electric lamp is equipped with a blown, glass lamp vessel1 having an axis 2. Around the axis 2, see FIG. 3, the lamp vessel 1 hasan end portion 3 with an end 4 where the lamp vessel 1 and a stem 5extending in the lamp vessel 1 are fused together. At a distance fromthe end 4, the end portion 3 has indentations 6 extending transverselyto the axis 2. The lamp vessel 1 accommodates an electric element 7, anincandescent body in the Figure, which is connected to currentconductors 8, 9 which extend through the stem 5 and issue from the lampvessel 1 to the exterior. The lamp comprises a lamp cap 20 with electriccontacts 21, a metal shell portion 22 which is undulated so as to formscrew thread, and a base portion 23 with at least one of the electriccontacts 21. The shell portion 22 is present around the end portion 3and the base portion transverse to the axis 2. The current conductors 8,9 are each connected with a respective one of the electric contacts 21.In the embodiment shown, wherein the lamp cap 20 is an Edison lamp cap,the shell portion 22 itself is one of the contacts. A coupling member30, see also FIG. 3, provided with cams 31 is present in the lamp cap20. Said cams 31 engage in a respective indentation 6. The couplingmember 30 is secured to the lamp cap 1.

The coupling member 30, see also FIGS. 3, 4 and 5, is a plasticsynthetic resin body of Liquid Crystalline Polymer in the embodimentshown, with a central portion 32 transverse to the axis 2, and,distributed around said axis 2, arms 33 extending axially from saidcentral portion 32, which arms each support, on an inner surface 34thereof, a respective one of the cams 31. At an outer surface 35, thearms 33 are provided with an undulatory profile which is in engagementwith the screw thread of the lamp cap 20.

In the embodiment shown, the central portion 32 of the coupling member30 is the base portion 23 of the lamp cap 20.

In the following Figures, corresponding parts bear the same referencenumerals as in FIG. 1.

FIG. 2 shows that the end portion 3 of the lamp vessel 1 of FIG. 1 hassix indentations 6 which are uniformly distributed around the axis 2.The indentations 6 jointly form basically an equilateral hexagon. Thecoupling member 30, see FIGS. 4 and 5, has at least three arms 33 with arespective cam 31. As shown in FIGS. 4 and 5, the coupling member 30 hassix arms, i.e. a through f, see FIG. 5, which jointly surround a regularhexagon. In an alternative embodiment, only the arms a, c and e arepresent. In a further alternative embodiment, the coupling member 30only has the arms a, b, d and e. These embodiments have the advantagethat a smaller amount of material is needed.

In FIG. 1, a snap connection is present between the coupling member 30and the shell portion 22 of the lamp cap 20, which snap connection locksthe shell portion 22 against rotation.

The shell portion 22 of the lamp cap 20 has an end portion 24 on theside remote from the lamp vessel 1, see FIGS. 1 and 3, and the couplingmember 30 has first axially directed elastic tongues 36 with hooks thatembrace said end portion 24 so as to form the snap connection. In theembodiment shown, six tongues 36 are present, however, this number maybe larger or smaller in alternative embodiments.

The central portion 32 of the coupling member 30 has an axially directedmeandering wall 37 in undulations of which the first axially directedelastic tongues 36 are arranged.

The central portion 32 of the coupling member 30 has a seating 38 for ametal bus which serves as the electric contact 21, see FIGS. 3 and 4.The seating 38 is in the form of a comparatively narrow, circular slit.

In FIG. 3, the metal bus of the electric contact 21 has a flaring edge25. The coupling member 30 of FIGS. 3 and 4 has second, axially directedelastic tongues 39 with hooks which, when the contact 21 is placed inthe seating 38, embrace the edge 25 so as to form the snap connection.

To provide the contact 21, the relevant current conductor 8, see FIG. 3,is arranged transversely over the central portion 32 of the couplingmember 30 and hence is clamped between the electric contact 21 and thecoupling member 30 after the contact 21 has been provided.

One of the current conductors, i.e. 9, is wrapped around at least one ofthe arms 33 of the coupling member 30, in the direction of the screwthread of the lamp cap 20, and clamped between said arm 33 and the shellportion 22 of the lamp cap 20 so as to form the contact thereof.

The lamp vessel 1, see FIG. 3, accommodates an exhaust tube 10 in thestem 5, which exhaust tube has a sealing 11.

The coupling member 30, see FIGS. 4 and 5, has six large openings 40 inthe central portion 32 through which the relevant current conductor 8,see FIG. 3, can readily be passed to the exterior during the assembly ofthe lamp.

1. An electric lamp equipped with: a blown-glass lamp vessel (1) havingan axis (2) and, around said axis (2), an end portion (3) with an end(4) where the lamp vessel (1) and a stem (5) extending in the lampvessel (1) are fused together, which end portion (3) has indentations(6) at a distance from the end (4), which indentations extendtransversely to the axis (2); an electric element (7) in the lamp vessel(1), which electric element is connected to current conductors (8, 9)which issue from the lamp vessel (1) to the exterior via the stem (5); alamp cap (20) with electric contacts (21), a metal shell portion (22)which is undulated so as to form screw thread, and a base portion (23)with at least one of the electric contacts (21), the shell portion (22)being present around the end portion (3) and the base portion extendingtransversely to the axis (2), and the current conductors (8, 9) eachbeing connected to a respective one of the electric contacts (21); acoupling member (30) provided with cams (31) in the lamp cap (20), whichcams (31) engage in a respective indentation (6), and which couplingmember (30) is secured to the lamp cap (20), characterized in that thecoupling member (30) is a plastic synthetic resin body having a centralportion (32) transverse to the axis (2), and arms (33) which aredistributed around the axis (2) and extend from the central portion (32)in the axial direction, which each support at an inner surface (34) arespective one of the cams (31), and which have an undulatory profile atan outer surface (35), which undulatory profile is in engagement withthe screw thread of the lamp cap (20).
 2. An electric lamp as claimed inclaim 1, characterized in that the end portion (3) has six indentations(6) which are uniformly distributed around the axis, and the couplingmember (30) has at least three arms (33) with a respective cam (31). 3.An electric lamp as claimed in claim 1, characterized in that thecentral portion (32) of the coupling member (30) is the base portion(23) of the lamp cap (20).
 4. An electric lamp as claimed in claim 1,characterized in that a snap connection is present between the couplingmember (30) and the shell portion (22) of the lamp cap (20), which snapconnection locks the shell portion (22) against rotation.
 5. An electriclamp as claimed in claim 4, characterized in that the shell portion (22)of the lamp cap (20) has an end portion (24) on the side remote from thelamp vessel (1), and the coupling member (30) has first axially directedelastic tongues (36) with hooks which embrace said end portion (24) soas to form the snap connection.
 6. An electric lamp as claimed in claim5, characterized in that the central portion (32) of the coupling member(30) has an axially directed meandering wall (37) in folds of which thefirst axially directed elastic tongues (36) are arranged.
 7. An electriclamp as claimed in claim 3, characterized in that the central portion(32) of the coupling member (30) has a seating (38) for a metal buswhich serves as the electric contact (21).
 8. An electric lamp asclaimed in claim 7, characterized in that the metal bus of the electriccontact (21) may have a flaring edge (25), and the coupling member (30)may have second, axially directed elastic tongues (39) with hooks thatembrace the edge (25) so as to form the snap connection.
 9. An electriclamp as claimed in claim 7, characterized in that the relevant currentconductor (8) is clamped between the electric contact (21) and thecoupling member (30).
 10. An electric lamp as claimed in claim 1,characterized in that one of the current conductors (9) is wrappedaround at least one of the arms (33) of the coupling member (30) in thedirection of the screw thread of the shell portion (23) of the lamp cap(20) and is clamped between said arm (33) and the shell portion (22) ofthe lamp cap (20) so as to form a contact thereof.